"Soups have a water base, which keeps the calories down. They tend to make you feel more satisfied, so you eat less," says Barbara Rolls, Ph.D., professor of nutrition at Penn State University and author of the forthcoming book "The Volumetrics Eating Plan: Techniques and Recipes for Feeling Full on Fewer Calories." Dr. Rolls led the original groundbreaking research that found that eating soup prior to your meal could reduce mealtime consumption by as many as 100 calories. However, "The soup itself must be fairly low in calories to be the most effective — otherwise you end up eating two meals," cautions Rolls.

Here are a few tips to help you choose the right soup.

FRENCH ONION VERSUS BROCCOLI-CHEDDAR SOUP
If you skip the bread and cheese topping (which can add 350 calories), your best bet is French onion soup, made with sherry, onions, butter and beef bouillon, at about 100 to 200 calories per cup, depending on ingredients. For instance, Au Bon Pain's has 80 calories per cup (keep in mind, the serving size is 12 ounces), whereas Panera Bread's has 220 calories per cup. And Applebee's French Onion Soup au Gratin has only 150 calories per cup, including a crouton and reduced-fat cheese.

On the other hand, broccoli-cheddar soup, often made with heavy cream, has about 175 to 275 calories per cup; Au Bon Pain's has 230 calories. Try to avoid cream and cheese soups in general.

CHICKEN NOODLE VERSUS CHICKEN VEGETABLE
While both are good choices, chicken vegetable is a bit lower on average because it's missing the noodles.

• Campbell's Kitchen Classics Chicken Noodle Soup (1 cup): 90 calories, 1g fat, 13g carbs, 6g protein, 870mg sodium
• Homemade chicken noodle soup, from scratch (1 cup): 300 calories, 7g fat, 28g carbs, 30g protein, 1,430mg sodium
• Campbell's Chunky Soup, Hearty Chicken with Vegetables (1 cup): 100 calories, 1.5g fat, 14g carbs, 7g protein, 790mg sodium

BLACK BEAN VERSUS LENTIL SOUP
This one's a close call. The only thing that really makes lentil a better choice is the sour cream that's often served on top of the black bean soup (60 calories for 2 tablespoons). Both of these legumes offer health benefits, including significant folate, magnesium, antioxidants, fiber and protein, with very low calories and fat. One additional benefit of black beans is the amount of iron, a nutrient many Americans tend to lack in their diets.

• Panera Bread's Low-Fat Vegetarian Black Bean Soup (1 cup): 160 calories, 1g fat, 31g carbs (11g fiber), 9g protein, 820mg sodium
• Goya Black Bean Soup (1 cup): 210 calories, 1.5g fat, 37g carbs (20g fiber), 11g protein, 1,050mg sodium
• Amy's Organic Lentil Soup (1 cup): 130 calories, 4g fat, 19g carbs (9g fiber), 8g protein, 590mg sodium
• Coco Pazzo Tuscan Lentil Soup (1 cup): 220 calories, 6g fat, 30g carbs (16g fiber), 15g protein, 610mg sodium

MINESTRONE VERSUS SPLIT-PEA SOUP
Peas are an excellent source of fiber, folate and potassium, but split-pea soup is usually the loser calorie-wise. It can be made a variety of ways, and when the peas are pureed, they're sometimes combined with butter and cream, which boosts the calorie and fat content. Minestrone, made with an assortment of vegetables, including leeks, carrots, onions, celery, potatoes, zucchini, tomatoes and beans, is consistently the better choice. One cup is generally in the 100- to 180-calorie range, depending on the amount of beans and whether pasta is added.

• Campbell's Kitchen Classics Minestrone Soup (1 cup): 110 calories, 0.5g fat, 22g carbs, 4g protein, 840mg sodium
• Health Valley Organic Minestrone Soup (1 cup): 100 calories, 2g fat, 17g carbs, 4g protein, 570 mg sodium
• Progresso Green Split Pea Soup (1 cup): 170 calories, 3g fat, 25g carbs, 10g protein, 870mg sodium
• Amy's Organic Split Pea Soup (1 cup): 100 calories, 0g fat, 19g carbs, 7g protein, 570mg sodium
• Au Bon Pain's Split Pea with Ham (1 cup, but serving size is 12 ounces): 140 calories, 1g fat, 23g carbs, 10g protein, 680mg sodium

CLAM CHOWDER VERSUS LOBSTER BISQUE
You might think all clam chowders are equal, but the Manhattan version is tomato-based, whereas New England clam chowder is made with milk or cream, which makes it higher in calories. But lobster bisque, typically made with heavy cream, can be the highest of all, coming in at 260 calories or more per cup, depending on the amount of butter, heavy cream and lobster used in the preparation. Bisque, after all, means thick and creamy, so what would you expect?

• Progresso Manhattan Clam Chowder (1 cup): 110 calories, 2g fat, 17g carbs, 6g protein, 880mg sodium
• Campbell's Kitchen Classics New England Clam Chowder (1 cup): 240 calories, 16g fat, 20g carbs, 5g protein, 720mg sodium
• Boston Chowda Lobster Bisque (1 cup): 260 calories, 19g fat, 12g carbs, 9g protein, 1,400mg sodium

HOT AND SOUR VERSUS EGG DROP VERSUS MISO SOUP
All these soups are excellent choices. P.F. Chang's Hot and Sour Soup (made with chicken and bean curd) has only 56 calories per cup. Egg drop soup has only about 60 calories per cup, and traditional miso soup has only about 40 calories per cup. Just stay away from the fried noodles that come with your soup!